This invention relates to an improvement in the electron optics column of an electron beam lithography (EBL) system and is particularly directed to an improvement in the magnetic deflection assembly of the electron optics column of an EBL system and to a method of making such an assembly.
In an electron optics column of an EBL system, also referred to as an EBL machine, the magnetic deflection assembly includes several magnetic coils spaced apart and arranged in a particular angular orientation. Its role is to position the electron beam accurately (on the order of a few hundredths of a micrometer) within a field whose size is typically on the order of millimeters. The beam position is determined by applying an appropriate amount of current to the magnetic coils making up the magnetic deflection assembly. However, because the coil windings have a non-zero resistance, heat is dissipated in the coils and the assembly. If the heat is not removed, the resulting temperature changes in the materials making up the assembly can cause the materials to expand and shift in position, and therefore affect the magnetic fields of the energized coils and hence also beam placement. The accuracy of an EBL system requires the magnetic field distortions due to thermal effects to remain small over the time required to calibrate the machine and complete writing on a substrate (typically tens of minutes). Thus, not only must the temperature of the assembly remain stable (&lt;=1 degree C.) over time, but the thermal response time must also be short (no more than a few minutes).
It is therefore an object of this invention to provide a thermally stable magnetic deflection assembly for use in an EBL machine and to improve such machines by the incorporation of such an assembly in the beam column.